Very shallow grade beam on micro piles in cold climate

[BubbaJ]

Project is a wood framed structure in a cold climate. Due to subterrainian constraints and environmental considerations, we cannot excavate a continuous footing to 42" frost depth. Proposed detail is to provide a 12"hx22"w grade beam supported on micropiles (depth to be determined.)
The proposed grade beam would penetrate the existing grade by 1 to 2" inches. The building slab would dowel into the grade beam.
Question is, do we insulate under the slab or allow the heat from the building to prevent the soil below from freezing?

 

[dcarr82775]

Can you build the gradebeam on a void form? This would eliminate any potential frost heave problems.

 

[BubbaJ]

Yes, we could. What would you suggest? Some type of compressible foam?

 

[dcarr82775]

There is a cardboard box literally called 'voidform'. It is primarily used for building on expansive soils. Only drawback is that being cardboard it will eventually go away so there would need to be something to seal the space.

There are also essentially styrofoam blocks that would also work. I can't remember any names but they come in various sizes and densities.

 

[dik]

You're looking for problems with 22" wide and 12" deep grade beam if subjected to cold. It's too wide and not deep enough to reinforce, except for the smallest of loads.

There are a couple of plastic void forms that I use. I typically use a product called 'Frost Cushion' by Beaver plastics. There is another product that I've only used on a couple of projects, I'll dig up the name... BARetired has referenced it a couple of times, but will dig up the product.

Dik

 

[oldestguy]

Consider burying a 4 ft. wide sheet of closed cell foam (pink stuff), extending out from the grade beam. We usually ask for that to be one foot down and place a section of that material against the foundation. the reason for burying it is in case someone wants plants along side the building.

A common thickness is 1-1/2", but it comes in thicker sheets. I'd not use it under a grade beam.

This along with void form ought to be belt and suspenders.

 

[oldestguy]

Oh, if you can place it on the exterior wall vertically, a common thing for house basements, then you can cover it with a hardboard, or brush on a mortar, since the stuff deteriorates in sunlight In the old days the hard board was asbestos board. There are new boards that do the job also.

Remember that grade beam is a good conductor of cold (reverse heat).

 

[dik]

Geospan by plastifab... the other...

Dik